The present invention relates to a drill and a cutting insert adapted for use in metal cutting.
A conventional drill 10 depicted in FIGS. 1 and 2 includes a steel body having a hollow shank 12 and a head 14 disposed at a front end thereof. The shank 12 has a central passageway 16 extending axially forwardly from a rear end of the shank and communicating with a pair of throats 18, 20 formed in a front face 22 of the head 14. Brazed in recesses formed in the front face are three carbide cutting inserts 24, 26, 28, two of which 24 and 26 are arranged at the throat 18. The third insert 28 is arranged at the throat 20. The inserts form respective cutting edges 24A, 26A, 28A that are arranged substantially on a diametrical line as viewed in FIG. 2. The cutting edges overlap radially during drill rotation, so that together they cut a bore. Chips that are cat become entrained in cooling liquid conducted forwardly through the central passageway 16 and the throats 18, 20 and are exhausted rearwardly within a gap formed between the drill and the wall of the bore being drilled. A pair of guide pads 30, 32 is provided in a side wall of the head 14 to guide the drill.
Another prior art drill 10' is depicted in FIGS. 3 and 4 wherein only two inserts 24' and 28' are employed. Such a drill may be employed to drill smaller bores than the drill of FIGS. 1-2.
During operation of the above-described drills, a drilling, operation produces a chip flow which tends to wear away portions of the front face of the steel head 14 situated between the cutting inserts, i.e., the portions 30A, 32A shown in FIG. 2 and the portion 30' shown in FIG. 4. The portion 30' shown in FIG. 4 seems, in practice, to be particularly susceptible to such wear. Eventually, erosion of the steel body can lead to a collapsing of the drill.
It would, therefore, be desirable to eliminate such a tendency for the drill to erode and collapse.